Functional analysis of the human inhibin alpha subunit variant A257T and its potential role in premature ovarian failure.

BACKGROUND

A nucleotide substitution in the inhibin alpha subunit (INHA 769G>A, A257T) has been associated with premature ovarian failure (POF). We hypothesize this mutation causes a reduction in inhibin bioactivity, removing its suppression on the pituitary FSH secretion. The aim of this study is to establish if A257T inhibin has reduced bioactivity.

METHODS

Mouse LbetaT2 pituitary gonadotrope, human granulosa (COV434) and human embryonic kidney (HEK293) cells were co-transfected with an activin-responsive reporter and increasing amounts of wild-type or variant A257T inhibin alpha subunit, and the degree of inhibin antagonism of activin signalling determined.

RESULTS

A 5-fold inhibition was observed with wild-type inhibin alpha subunit overexpression (P < 0.001) (confirmed in HEK293 cells), while the A257T inhibin showed no inhibitory activity. In human ovarian COV434 transfected cells, while wild-type and A257T inhibin A had similar bioactivities, there was a significant reduction in the bioactivity of A257T inhibin B compared with wild-type inhibin B (P < 0.005). In all the three cell systems, overexpression of wild-type and A257T alpha subunit resulted in a 2- to 6-fold increase in secretion of dimeric inhibin indicating the reduced inhibin response was not due to a failure of dimerization.

CONCLUSIONS

This study supports the hypothesis that the INHA 769G>A variant may increase susceptibility to POF with impaired inhibin B bioactivity and provides insight into the complex aetiology of POF.